Rabat , Morocco -LRB- CNN -RRB- -- Morocco 's Interior Ministry said Thursday that three Moroccan suspects loyal to al Qaeda have been arrested in connection with last month 's bombing at a popular Marrakech cafe , the official Maghreb Arabe Presse news agency reported .

One of the suspects was described in the Interior Ministry statement as the main figure in the April 28 bombing that killed 16 people and injured 21 , according to the MAP report . The ministry statement described the bombing as a terrorist attack .

The bombing occurred around 11 a.m. at Cafe Argana in Marrakech 's old city , which is designated by the United Nations ' cultural arm as a World Heritage Site . Tourists flock to the old city this time of the year , and it is usually packed with stalls , storytellers and snake-charmers .

World leaders , including U.N. Secretary-General Ban Ki-moon and U.S. Secretary of State Hillary Clinton , condemned the bombing .

`` The individuals were absorbed by jihadist ideology , and had allegiance to al Qaeda and had already made several attempts to join some of the hotbeds of tension , especially Chechnya and Iraq , before deciding to carry out terror in the homeland , '' the ministry statement said , according to MAP .

The suspects learned on the Internet how to make the two remote-detonated explosive devices used in the bombing , the ministry statement said . The attackers chose Cafe Argana as the target because of its popularity , and dressed as tourists to access the area , the statement said .

A preliminary investigation found remnants of explosive materials and tools `` that had been discarded after the terrorist act , '' according to the statement .

CNN 's Mitra Mobasherat , Salma Abdelaziz and journalist Martin Jay contributed to this report

@highlight

The Interior Ministry says the suspects are Moroccan

@highlight

The April 28 bombing killed 16 people at a popular Marrakech cafe

@highlight

The suspects used the Internet to learn to make the bombs , the ministry says